text:
What's the most commonly used circling approach procedure in the US National Airspace System?
As the title says: which of the many circling approaches in the US National Airspace System holds the title of "circling approach that is flown most frequently?"  My guess is it's the KTEB ILS 6, circle to RWY 1 procedure, but I don't know what other circling approaches in the NAS are frequently/commonly flown aside from the ones at KASE, which aren't really within the scope of this list, since the only reason they don't have straight-in minima is due to the excessive descent rate required for a straight-in approach.
As to why I'm asking this: it seems that the Part 142 training and ATPL checkride standards for circling approaches are causing a bunch of negative learning, as the training too often asks jet pilots to throw stabilized approach criteria in the dustbin.  As a result, I was thinking it would be better to use a realistic form of circling (such as KTEB ILS 6 circling to RWY 1) when testing the ability of line ATPLs to fly circling approaches "in the box", as opposed to the downright unrealistic setups currently used (such as KMEM or KJFK, where the circling procedures are never actually used), as well as using night visual conditions for circling training and checking vs. trying to make people circle at minimums, which is dicey at best given current circling minimums.

Maybe a better question would be to ask which circling approaches have the most accidents.  There might be actual data there from the NTSB.  The sim training should aim to figure out what happened and how to prevent it.  Current FAA standards require the visual systems to be adequate for the pilots to keep the airport in sight.  This would preclude most circles to the opposite runway.

This is not information you are likely to find anywhere mostly because its not really recorded by anyone but individual pilots and there is no regulation (that I know of) to report these statistics out to any authority.
But I think there is a misunderstanding in your question, circling approaches are flown in many cases and there are lots of instances where they may be used at lots of airports, here are some examples Ive encountered in practice:
Some airports only have approaches to one runway like KDXR only has approaches into RW08 due to terrain but the winds most generally favor RW26. Thus its not uncommon to utilize the 08 approaches and do a north bound circle to land to 26.
One of the most common "circle" requests I have made was the time I spent flying out of KOAK. The hangar was off the end of RW15 but generally traffic is sequenced in to RW30 or RW28L/R. If its IFR (or even on a VFR day) and I had the minimums I would "circle 33" and roll out right to the hangar. This was a matter of convince for not only me but kept my little PA-28 out of the taxi ways the big boys were using.
Before the RNAV/GPS days which made it much easier to chart approaches into fields there were less approaches. Since there is no GPS requirement for IFR operations in the NAS there are plenty of IFR capable aircraft flying out there that can only fly ILS/LOC/VOR approaches. For example KDYL only has a VOR approach into (the general direction of) RW 24 since its a VOR-A level approach which only has circling minimum. The winds there are highly variable and you are likely to often have to circle to RW05 if you don't have GPS to fly the RNAV approach.
Training scenarios are not always created because they are used frequently but because they test challenging situations. Flying a circling approach at KJFK may be more difficult but thats the point, if you can fly that you can easily fly the ILS to RW1 at KTWB then circle to land RW06.

+1 for the final paragraph.


text:
Can one fly up side down while a glass of water keeps full due to g-forces?
If one makes a looping for example with a plane and the g-forces that the planes makes will keep the water in the glass, but if one is at the top of the loop is there still enough g-force to keep water in the glass?

OTOH you can empty the glass without inverting the aircraft at all, just by suddenly and forcefully pitching down.

Not only can you keep a glass of water full, you can pour one (or tea) while rolling the aircraft yourself if you're Bob Hoover! https://www.youtube.com/watch?v=V9pvG_ZSnCc

https://www.youtube.com/watch?v=g99ho_ExApU

Yes, as long as you continue the loop, and don't fly the plane in the upside-down position.
See, for example: Barrel roll with a glass of water on a glider

but the question was in 'upside down position' isn't it possible than?

@Marijn I think what Doppelfish is referring to when he says "don't fly the airplane in the upside-down position" is that you don't try maintain level inverted flight. In other words, don't ask the wing to generate lift opposing gravity at the top of the loop.

It seems mandatory to post Bob Hoover Pouring Tea Roll:  https://www.youtube.com/watch?v=V9pvG_ZSnCc

Can one fly up side down while a glass of water keeps full?

Yes, but given the speed of the aircraft, it must fly a more or less tight loop. For an aircraft at 160 km/h the radius of the turn must be smaller than 200 m. On the other hand for a fighter at 500 km/h, the radius may be as large as 2 km.
In both cases the force due to the turn is 1G positive (assuming the turn is "nose up"), that is the body and objects within the aircraft are pulled towards the outside of the turn. When they are at the topmost point of the turn, this force is vertical towards the sky, this 1G balances exactly the gravity and everything is weightless, as this dog.

Aircraft flying a vertical loop with a glass of water:

The interesting instant is when the aircraft reaches the top of the loop. Forces on water:

Are gravity force and force due to normal (centrifugal) acceleration.
Are proportional to the mass of water.

We must balance gravity
To prevent water from flowing out of the glass, forces exerted on the water must have a resultant (sum of vectors) which is going away from the ground.
As both forces are proportional to mass and accelerations, we can remove the water mass from the equation, and just keep the accelerations. This means we need to have a normal acceleration equal to or greater than gravity acceleration.
Calculation of the normal acceleration
Gravity acceleration is indeed a fixed value: 9.81 m/s².
Normal acceleration $a_c$ itself is proportional to the radius $r$ of the loop and the angular speed $\omega$ of the aircraft (the angular speed is the RPM, but expressed in radians per second): $a_c = \omega^2r$. So to prevent being watered, we need to have an angular speed such that $a_c \geq g$, that is $\omega^2r \geq g$
On the other hand we can express the angular speed as a function of the radius and tangential speed $v$: $\omega = v/r$ and now our constraint $\omega^2r \geq g$ becomes: $v^2/r \geq g$ or $v \geq \sqrt {r \cdot g}$.
Back to speeds and RPM
Given a radius, we must fly at some minimal speed to neutralize gravity. Or given a speed we must decrease the radius to a maximal value. Here is a table for some values of radius. At the corresponding speed normal acceleration balances gravity (the number of loop rounds per minute is also mentioned).

Example: For a radius of 50 m, we need to fly at 80 km/h or higher. Or if we fly at 80 km/h, the radius must be 50 m or smaller. The corresponding angular velocity to 80 km/h is 4.2 RPM.
Flying at a higher speed or with a smaller radius will just push water deeper in the glass.
Special request for @DeltaLima, when flying a loop the size of the Earth, (well in practical this means flying horizontally but inverted), then to prevent gravity to empty the glass, you need to fly in excess of 28,000 km/h. That's what they do in the ISS. I guess we closed the loop on the topic.

When you mention RPM, I immediately think of engine revs.

It becomes interesting when the radius is equal to earth's radius. Then you can really fly upside down whilst keeping the water in the glass. You have to "fly" close to 8 km/s to achieve that.

^28800km/h I'm wondering where you have found this "fact". 8km/s on a circumference of a supposed ball of 40075km. Very interesting, yet very theoretical and not proven, hence, not reality.

@NormLDude: It's the result of the formula in the answer  ($v = \sqrt {r \cdot g}$) which gives 7.9 m/s or 28,460 km/h at sea level). All LEO satellites are orbiting at this speed around our planet. For instance, the ISS is currently at MSL + 402 km, orbiting at 27,630 km/h, a bit slower because the gravity is a bit lower.

If the loop is continued, the G at the inverted position is a function of airspeed and AOA demand on the aircraft (and the resulting nose track).  If the airspeed is allowed to decrease near stall speed, it is possible for the aircraft to experience less than 1 equivalent G (causing the water to pour out of the cup).  If the pilot flys the loop to allow for 2Gs across the top of the loop, the pilot will feel 1G into the seat (2 total Gs minus the 1G of God's G), allowing water to stay in the cup.  Really, 1.01 G inverted at the top of the loop will result in a 0.01 equivalent positive G, keeping water in the cup.

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text:
Is there a system of automated sharing of current (experienced) weather between aircraft in flight?
For example, if say - Aircraft 1 is flying a certain route, being followed by Aircraft 2 at an interval of say, 5 minutes (over the same position). Is there a system by which Aircraft 1 can transmit the weather it is experiencing at that moment to Aircraft 2? Something like crowd-sourcing weather from all on-board sensors of aircraft in the air? Akin to ADS-B for weather?

The closest thing that I know of right now is a PIREP, but its not automated and not "peer-to-peer". The only automated aircraft peer-to-peer communication I know of is for the TCAS system.

Possible duplicate of The practical use of streaming data received from sensors installed on airplane

In addition to the PIREP system alluded to by @RonBeyer, PIREPs and other weather discussed on ATC frequencies is effectively available to all crews monitoring that frequency. ATC also tends to serve as a weather report aggregator and distributor, especially for such items as ride reports, icing, and cloud tops and bases. Other than these, there is currently no other system in place. It would be great if there were something such as what you describe. The PIREP system needs a major overhaul.

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text:
Which organisation deals with Aviation Law - IATA or ICAO?
Both Organisations are involved in Aviation Regulation. But which of them deals with Law? Are directives given by both equally applicable to all aircraft & airline operators?

Related: What body creates legally binding aviation regulations in Europe?

As far as I'm aware, neither of those organizations is involved in law.

ICAO does deals with law, although not directly.
The Convention on International Civil Aviation and its 19 Annexes form the basis of International Air Law. Although the Convention text itself is not directly a law, the 193 ICAO Member States ratify the ICAO Standard and Recommended Practices, albeit sometimes with minor modifications.
From this answer:

ICAO is the International Civil Aviation Organization, a specialized
agency of United Nations. It was created after the Convention on
International Civil Aviation (the Chicago Convention) of 1944 was
ratified in 1947. The purpose of ICAO is according to the convention:

"WHEREAS the future development of international civil aviation can
greatly help to create and preserve friendship and understanding among
the nations and peoples of the world, yet its abuse can become a
threat to the general security; and
WHEREAS it is desirable to avoid friction and to promote that
co-operation between nations and peoples upon which the peace of the
world depends;
THEREFORE, the undersigned governments having agreed on certain
principles and arrangements in order that international civil aviation
may be developed in a safe and orderly manner and that international
air transport services may be established on the basis of equality of
opportunity and operated soundly and economically;
Have accordingly concluded this Convention to that end."

Within ICAO, the 191 Member States and a number of global aviation
organizations work together to develop international Standards and
Recommended Practices (SARPs). These SARPs are the reference for
states developing their national civil aviation regulations which are
legally enforcible. This is an important aspect: ICAO SARPs are not
legally binding by themselves, they form the basis of national
regulations which have legal status.
In this way civil aviation regulations are harmonized all over the
world, with slight differences based on the actual implementation in
national regulations. These local differences are then reported back
to ICAO and published.

IATA is a trade organisation representing the interests of their member airlines. They don't deal with law in the sense that their directives are not embedded in law.

Neither.
IATA is a trade association of  airline operators (International Air Transport Association). It's main focus is to support aviation with global standards for airline safety, security, efficiency and sustainability. (IATA website)
ICAO (International Civil Aviation Organization) is an agency of the United nations. The ICAO Council adopts standards and recommended practices concerning air navigation, its infrastructure, flight inspection, prevention of unlawful interference, and facilitation of border-crossing procedures for international civil aviation. ICAO defines the protocols for air accident investigation that are followed by transport safety authorities in countries signatory to the Chicago Convention on International Civil Aviation (Wikipedia).
IATA or ICAO do not have legislative powers. The members of the organizations are commited to act according to the standards , rules or such set by the aforementioned organizations, but as such they cannot be considered to hold the authority and influence of law.
Simply put, the signatory states of ICAO have adopted ICAO standards into their own laws, rules and regulations, thus effectively making them legally binding.
If you operate a plane in an ICAO member state, you pretty much have to do it as ICAO has thought it would be best to do. If you choose not to, ICAO can't do sh... nothing about it, but your local law enforcement most likely can.

That is true, but ICAO member states are sovereign, ICAO has no jurisdiction "inside" member countries. Member states just have agreed to abide by what ICAO says. Well, basically any law is a matter of contract, I might as well decide I do not respect the laws of my country, heck, quite a few ppl actually do so

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text:
How do you control a 500mph model plane?
This video was posted as an answer to another question:

The plane is quite hard to even see due to traveling at a high speed in a tight loop. Is it actually being actively controlled around that loop, or is it just a question of getting the control surfaces to the right attitude then watching the wind accelerate it it round and round the loop?
I can see the wings have been painted in contrasting black and white against a bright orange body, but are there any other techniques or "tricks" to giving the pilot feedback from the plane's position and attitude?
(I'm aware that FPV exists, but it doesn't seem to be used for planes very much compared to drones, is that correct?)

Unless you can determine the field of view, it's difficult to evaluate what you would see with naked eyes. Modern cameras have very small sensors, and short focal lengths, so large fields of view. That's why the moon is so small in movies and on photos. Even with a "normal" ratio, you don't see any details you would see with eyes. You can check with your smartphone next night, it will be even smaller.

I think it would be good if the question acknowledged that this 500+ mph r.c. aircraft is an unpowered glider!  Anyway, it is definitely being actively controlled by the pilot-- there is no possible control position that results in fully automatic self-sustaining back-side-of-the-hill dynamic soaring!  What sort of amplitude of control inputs are involved?  -- that sounds like the basis for another question--

This video shows how such a model aircraft is controlled from the pilot's perspective:

The pilot manually controls the plane from launch to landing, and also during the loops he actively moves the sticks to keep the plane  in a controlled loop.
Just setting the controls and watching the wind accelerate it will not work, because throughout the loop, the airspeed as well as the relative direction of gravity changes. So you can observe that the pilot pulls up the elevator more to turn out of the tailwind back away from the ridge, and also makes small corrections in roll, pitch (and yaw on some models) to keep the plane in the sweet spot on the slope, preventing it from drifting away as a free flying model probably would.
In terms of "tricks" the pilot is always flying the same circle so he knows where to expect the airplane's orientation and position. What likely is more difficult than sustaining the loops is getting back to the landing site from far out, because the silhouette of the plane can correspond to two different attitudes, like how you can interpret a 2D projection of a 3D cube in multiple ways. Pilots usually overcome this with experience, the last known attitude of the aircraft, or giving gentle control inputs to figure out which way the plane is responding (see https://forum.flitetest.com/index.php?threads/aircraft-orientation-and-overcoming-optical-illusions.64027/).
(FPV is becoming common on other fixed wing model aircraft (e.g. long range or park flyers), but in the case of dynamic soaring it does not seem helpful because you'd repeatedly see blurry ground, blue sky and overexposed sun every 2 seconds.)

Welcome to Aviation SE, txp.  Great first answer!

You could also mention control rate settings.  No doubt at 500 mph the control surface deflections would be tiny.  Amazing how that glider can withstand all those G's looping so tightly.

Re "yaw"- are we certain that this aircraft even has a rudder at all?  Looks to me like the pilot's left hand is just resting there helping to hold the transmitter.

Hi Camille, thanks for the edit!

Re control rate settings: I'm sure the pilot uses tons of expo or maybe even a rate switch to deal with the different flight regimes, good point! However, I feel like this goes beyond the scope of a basic answer to the question. Feel free to add more detail in a footnote or so though!

Re yaw: I agree, from the two videos it looks like this particular plane does not have a vertical control surface. Maybe it's common for DSS planes to fly with elevator, aileron and flaps only to save complexity and weight, but am not familiar myself. Have put yaw in parentheses

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text:
Does the NTSB ever not follow up a preliminary report?
Two years ago, there was a fatal crash in Fredericksburg, VA in which 6 people died in a Beech 95-B55. For some reason, the story struck me, and I wrote a note to myself to follow up on it.
The NTSB published a preliminary report 12 days after the crash (on 8/24/2016) but has not published any report since then. Do investigations sometimes end at preliminary reports, or will they someday follow up with a final report?
The NTSB case is ERA16FA288. I searched the NTSB's "Aviation Accident Database & Synopses" page for all events in Virginia on 8/12/2016 (as well as googling the airplane's tail number), and couldn't find anything after that preliminary report.

Yes, there are many cases where the NTSB doesn't release a "final" report. There are also cases where the NTSB doesn't release a final report for years. You could try to contact the Richmond FSDO to ask about a status.

Looks like the final report was published Oct 1, 2018.

https://aviation-safety.net/wikibase/189245

As a retired NTSB employee, I can say that reports with an FA number like that one should definitely close out with a probable cause determination, typically within a year.  Two years is an outlier, and the delay is likely attracting some internal attention.  If you really want to find out about the status, you can call 202-314-6290 and ask for the Ashburn field office.  It's probably their case, and the manager should be able to figure out what's holding it up.


text:
How can the breath of a pilot be recorded?
On a plane, as a passanger, I can't hear my own breath. I can't hear my own breath even in a silent room.
On a plane, there is a continous background noise.
And the microphone recording the noises in the cockpit, are probably not directly at the lungs of both pilots.
I am really wondering, how can the breath of a pilot simply be recorded on the cockpit, if it wasn't designed specifically for that (or it isn't a very high quality recorder placed directly to the body of the pilots)?

Breathe heavily onto a microphone. You'll definitely hear it (provided it doesn't have a filter to remove such noise.) I've certainly heard my own breath in my aviation headset plenty of times.

Wat? You can't hear your own breath? I can hear mine all the time (tho I ignore it).

@bjb568 Now I tested it. On normal circumstances, I can't hear it even in a silent room. But a little bit of elevated breathing intensity (for example, walking up a floor) makes it hearable. But on a mobile talk, I never hear the breath of the other side.

@reirab It is true. But on mobile talk, I never hear the breath of the other side.

@user8558 If they're breathing hard enough, you can hear it. Funny thing, we actually had that happen during a phone interview with a dev candidate once. Sounded like he was out of breath. You generally can't hear it with phones, though, since people usually hold the mic to the side of their mouth instead of directly in front. Aviation headsets usually have the mic directly in front of your mouth.

@user8558: part of the reason for that is that mobile phone audio is heavily compressed, in ways cleverly designed to selectively discard information that "doesn't sound like a voice". But listen to any Muse song and you'll hear that good-quality microphones can pick up breathing ;-)

Pilot's breath is not recorded on a flight data recorder, as it is not one of the data parameters.
However, if a pilot is breathing abnormally, the cockpit voice recorder may easily detect that as the breathing sound is captured by the CVR.
A reference to this can be found in the press conference summary for Germanwings flight 4U9525, which states:

... the only sound to come from Lubitz is the sound of him breathing,
  picked up by the microphone on his headphone set. ... “We could hear
  human breathing inside the cabin,” said Mr Robin, “and this breathing
  noise we heard up until the moment of final impact. That means that
  the co-pilot was alive. Apparently he was breathing normally, so this
  is not someone having a heart attack, for example.

Someone having a heart attack wouldn't usually set the auto-pilot to an altitude of 100 feet over mountainous terrain.

@davidjwest, No, but it would be conceivable for them to slump over onto the yoke (in an aircraft that has a yoke, at least.)

I'm not sure why you mentioned the FDR?

One of the channels of the Cockpit Voice Recorder is the microphone on each pilot's headset. This is much closer to the source of the breathing noise than your own ears. The microphone may also not have a wind filter so breathing on it will generate a lot of noise.

You can actually hear breath on the mic (see ratchet freak's answer above). If you have multiple pilots, you can hear the other guy breathing on the channel intermittently. You do not hear every breath, just the sniffs, intakes, coughs, etc, all the little noises he makes.
In other words, when they say "breathing" for that incident, that includes all kinds of little noises that are associated with normal breathing.

I wonder if perhaps the CVR records audio even when the squelch function is suppressing it from being played to the headsets (because no one is talking?) In that case, they'd probably be able to hear almost every breath on the recording.

@reirab The CVR only records what is on the channel. Squelch is only applicable to received transmissions (which have noise). The pilots can hear each other clearly. As I said normally you can't hear somebody breathing, but you do hear little noises. For example, even if the other guy just opens his lips you might hear a tiny little smacking sound. Typically what you hear are: sharp intakes of breath, yawns, swallows, little coughs/throat clearing, sniffs/sniffles, sighs/heavy exhales.

I haven't flown any airliners, but in the PA-28 I fly, there's a squelch on the mics just for intercom, too. It mutes when no one's talking in order to prevent background noise (and breathing noise) from being played in your ears constantly. It automatically unmutes above a certain volume level (e.g. when someone talks, breathes hard, coughs, touches the mic, etc.) There's a separate squelch for received transmissions on the COM radios.

@reirab Now that you mention it, I guess there is a second squelch for the intercom. I usually turn that off because I find it difficult to get it exactly right. It is always cutting off the other guy's voice, especially if he says something softly. The CVR will obviously have no squelch, so anything you would hear with squelch off, I would expect to be on the CVR.


text:
How to calculate the fuselage geometrical parameters?
How I can calculate the fuselage midsection having a constraint length? Also, if I want a cross section shaped like an Antonov that on top of it have a lower ratio than the bottom, as that is part or can do the calculations to determine the area in front.

There is no straight answer or a formula for this one. In real life you first think of what you want to fit inside the fuselage and then design the rest of the plane. For airliners that would be space for passengers and luggage as well. Different fuselage shapes come straight in line from the requirements that the airplane is supposed to meet. Antonov has the shape you described, because it needs a lot of space inside and should stay low to the ground, so it's wings are mounted on top. It also has a huge weight, so a strong set of wheels is required - hence the shape at the bottom (to create enough space for the landing gear to hide without taking the loading space)
Apart from functional requirements, designing a fuselage must take many different aspects into consideration (starting from the most important - but of course the hierarchy depends on many factors):

mass
drag - the frontal area is not all, it is also the nose shape, wing connection and overal area wchich results in friction loses
stress caused by wing's lift and drag, momentums of wing and stabilizers and pressure difference
fatigue safety
doors, windows, landing gear


text:
Why is the trailing edge sweep angle smaller at the wing root?
Many airliners have a distinct unswept part at the wing root at the trailing edge. See for example this image from Wikimedia of a B737-400.

Other examples include the B777, A320, Embrear 145, and many more. Virtually all airliners have at least some degree of less sweep at the wing root.
Why is there a part of less sweep at the wing root (to facilitate engine mount; Aerodynamic reasons)? Why does a completely unswept part seem to be a preferred choice for this part of less sweep, as opposed to any other sweep angle than zero?

Related, or perhaps duplicate: http://aviation.stackexchange.com/questions/11704/what-is-the-aerodynamic-benefit-of-trailing-edge-sweep

Definitely related, @ROIMaison, but not really duplicate. Once I read this Q & Jordy's A I could make a duplicate out of the other, but without his answer, the other Q&A didn't really address this specific question. At least, not to me.

There are two main reasons:

Swept wings suffer from interference at the center of the wing. If wing taper and sweep remain constant over the full span, the lift distribution will show a distinct drop at the center. This is called the "Mitteneffekt". The remedy is to locally increase the wing chord near the root and to decrease the wing's sweep angle. This, together with a change in airfoils and local incidence, "fills up" the dimple in the lift distribution and reduces induced drag.
Large aircraft need heavy wing spars, and increasing chord near the root gives the spar more height while the relative thickness of the airfoil can remain unchanged. A higher spar is structurally more efficient, so increasing its height at the root saves weight. Since the relative thickness determines the maximum operating Mach number, it cannot be increased locally without hurting the whole wing. The better alternative is to disproportionally increase wing chord at the root.

The unswept trailing edge near the root is a consequence of Boeing's flap track mechanism. Boeing Fowler flaps move perpendicular to the hinge line, and an unswept hinge line avoids lateral movement of the flap. Another consequence is a gap between the inner and outer flaps in order to allow both to move back without colliding. Boeing fills the gap with a high-speed aileron. Also, this gap avoids that the flaps protrude into the hot, turbulent exhaust stream of the jet engine.
Airbus flaps move in flight direction and leave the sweep angle of the trailing edge free. Also, they don't need a gap between the flap segments left and right of a sweep change of the hinge line.

These are more important reasons indeed. I'll change my answer to 'minor reasons'

Two other (minor) reasons for this:
Landing gear storage
The main landing gear is positioned just behind the aircraft's center of gravity. For most aircraft with wing-mounted engines this is near the trailing edge of the wing root. In order to have enough space for the landing gear when it is retracted, and to have a part of the wing structure that is dedicated to support the landing gear, this part of the wing has a larger chord, and thus a smaller trailing edge sweep angle.
Flap effectiveness
Another benefit of a low trailing edge sweep angle is that the effectiveness of the inboard trailing edge flap is higher. The maximum $C_L$ of the flaps decreases with increasing sweep angle. (http://adg.stanford.edu/aa241/highlift/clmaxest.html)

I'm guessing that flap effectiveness was more a driving factor in this kind of wing platform as you see a similar arrangement on Soviet-era airliners whose gear retracted into mid wing pods.

These are relatively minor factors compared to what Peter (both Peters, actually) mentioned later.

I think it is also about arranging the wing spars. Due to the swept wings they meet at an angle in the middle and must handle a high torque. This can be reduced by either having an A connecting piece or leading the spar in the unswept part.

I think this is not the case. As far as I know, the wing spars are either located parallel to the air flow, or they change direction at somewhere in the wing. Anyway, the root trailing edge is not a part of the wing box. example: an A320 wing


text:
How to prevent dizziness when thermalling in the back seat?
I recently started learning to fly sailplanes. I am usually quite resistant against airsickness, both when flying commercially as well as flying in the front seat of a sailplane (either when the instructor is thermalling or when I do it myself). However, I recently took a longer flight as a passenger in the back of an ASK-21, and found that I got quite dizzy as the flight progressed. The thermals were not great so we were circling quite tightly to climb at all. It was only when I was offered the controls that the feeling of airsickness disappeared (surprisingly rapidly, too, even though we were still circling, porpoising, etc.)
What are some techniques to mitigate airsickness, specifically in the back seat of a sailplane, other than simply taking the controls?
Things I tried:

Looking forward: more difficult due to limited visibility, especially straight ahead. What would be a good point to focus on?
Take deep breaths: resulted in hyperventilation symptoms (tingling of hands and face).
Stick in hand: helps a little, but I don't want to disturb the pilot flying.

Minor point, but is "dizzy"/ "dizziness" really the right word?  Such as a sense that the world is spinning even when you are flying straight?  Or do you really mean "queasy", i.e. a sense of nausea?

@quietflyer A bit of both I think.

Motion sickness is a somewhat complicated mechanism with a lot of variables, and ones propensity to get motion sickness may vary substantially even within the same day.
Over time most people will get accustomed to circumstances that trigger motion sickness, most common ways to prevent/manage/treat motion sickness are:

Focus your view at distant objects, do not look close (gauges) for long periods of time
Antihistamines, unfortunately only ones that cause drowsiness help, so they are ruled out in aviation
Scopolamine patches
Acupuncture wristbands
Diet: somewhat counterintuitively an empty stomach is very bad when it comes to motion sickness
diet subcategory: eat/drink ginger (moderately) pre-flight (thanks to Ralph J for a reminder)

For me personally I've found that the "distant gaze" and diet methods work very well. I easily get motion sickness unless I'm at controls, be it a plane or a boat. Focussing on surroundings as much as possible, and eating moderately before entering a situation that might agitate motion sickness will prevent any symptoms with almost hundred percent effectiveness. Of course, your reactions might vary.
Quick googling gave this site with pretty correct, complete and concise wrap on the subject: Cleveland Clinic - Motion Sickness
P.S. fun fact: some pilots get motion(less) sickness if the fly in a stationary simulator. They are so accustomed to how real flying feels, that they are thrown off the other way around.

Diet is indeed important. The only time I got sick in the backseat of a two-seater glider was after having had three steaks for breakfast.

Might consider expanding content on antihistamines-- might be a viable option in this case as the person is not the PIC and will not be the primary operator of the controls--

@quietflyer I wonder if that would put PIC in a predicament, as he/she  should not give control of the aircraft to a person who is under the influence of a drug that may affect performance in an adverse way?

Many sources add ginger as helpful, either ginger snaps or ginger ale, or however else you like it.

When sailing a small boat in heavy chop, if someone starts getting quiet and green-faced, we put them on the tiller (if capable) and definitely make them look at the horizon.

The wrist bands are a placebo.  In other words, they do not work.

@AnonymousPhysicist even if the effect is placebo it still might work for some people. Does not matter what the mechanism is.

@AnonymousPhysicist placebos often work via the placebo effect.

@AnonymousPhysicist Actually the leading acupressure and acustimulation bands have been shown to be effective in several independent studies, including when placebos are not effective.  However, they do not seem to work for everyone, and also correct use for untrained users has proven to be a problem for some of these products.

@RBarryYoung Your link says under "discussion" that they don't work.

@Jpe61 If you look at the link above, in RBarryYoung's study it says placebos don't work for motion sickness.  Also, you shouldn't have to pay more than the price of sugar to get a placebo.  I checked a Cochrane Review when I posted this and it was quite clear that all studies of these devices are flawed and the results are inconsistent.  That means they don't work.

It would seem that there is no scientific proof and/or consensus either way. As long as some people find it works, it works.

As @Jpe61 says there's a lot of variables and variability with motion sickness and what works for one person may not work for another. That being said from my own experience and speaking to others who do aerobatics there's a few things that seem be consistent:

Exposure: as you fly you will get used to the motion, up to a point
Diet the night before matters quite a bit: gut-bombs the night before can make your stomach more sensitive the next day. Avoiding heavy alcohol consumption the night before is good too. Massive beer and curry bashes aren't conducive to happy flying
Carbonated drinks: some people say they help settle the stomach, others just the opposite, I'm one of the latter
Keep cool: getting too warm causes queasiness, fresh air is good too

good points on the carbonated drinks and fresh air!

Not enough to warrant a full answer: stay hydrated! I drink cool, flat table / tap / bottled (doesn't really matter) water continuously, but not so much it starts sloshing around in my stomach. Some of my favorite airports have water fountains at every gate where you can fill up your water bottle. I also want to second (third?) the advice on fresh air. In airliners, the first thing I do even before sitting down is open the vent all the way and turn it such that it blows directly in my face with the seat upright and directly past my face with the seat reclined. Obviously, a glider doesn't have

… AC, but maybe you can find something to accommodate you nonetheless.

I would say it mostly requires desensitization from exposure.  In other words, stick it out until you get used to it, and find ways to get similar exposure on the ground to speed up the process.
The problem is mostly conflicts between G load sensations and sight picture, and inner ear cochlea fluid reactions to sustained rotations in space, such in a sustained turn where the fluid catches up to your rotating head, then when you stop turning the fluid continues moving, giving you a sense of turning the opposite way.
It's mostly the conflict between your inner senses and the sight picture that makes you dizzy.  You can get the same (somewhat milder) effect with precisely the opposite stimuli in an IMAX movie, where the sight picture that dominates your vision field, the screen being so big, shows you turning in flight, but your inner ear is telling you you're stationary.
Some people get better by removing the visual stimulus, by closing their eyes, or by changing their visual focus. In your case all it takes is to distract your brain with a task like flying the glider.
Two possible desensitization techniques you can do on the ground is spend time on a park swing to desensitize yourself to G load variations (helps with seasickness), and spend time on a something that can be made to rotate with little effort, like an office chair or barstool with a really good low friction pivot, where you can sustain a rotation for extended periods and stop them at will. Just keep doing it and you'll find you can tolerate the movements more and more over time (for extra fun and entertainment, set up a continuous rotation for a minute or two, then stop it and stand up - make sure there is something soft on the floor to land on as you leap sideways).

Well worth +1, but it is really hard to mimick the sensory environment of flying. The swing method might really work though!

The spinny chair thing is a common ground school demonstration of vertigo from instrument flying.   You close your eyes and put your head up and down as the chair is gently rotated, then told to open your eyes and stand up right away.  Everybody will generally stand at about a 45 deg angle and fall over.  It's the sustained turn, then stopping the turn, that gets you into trouble, and you can replicate that in a chair.  The swing is to desensitize to 0 G.  I'm fine in planes, but more than 15 min on a park swing gets me queezy.

In my limited experience, always look the way you’re turning, lean into the turn to the extent that you can.


text:
Is a question mark in a TAF forecast ever valid?
One will sometimes see a question mark in the body of a TAF (Terminal Aerodrome Forecast), such as in the second line below:
TAF MDLR 162200Z 1700/1800 00000KT 9999 SCT018
  PROB30 1704/1710 8000 ?SHRA BKN016
  BECMG 1713/1715 07010KT

Is there any time that this is correct, or should it always be considered a typo when it is encountered?  I haven't found any references to such an annotation while searching online, but those resources tend to be FAA-centric, and if other weather reporting uses that punctuation to convey a specific meaning, I'd be interested to know about that.

@757toga Good thought on that.  The decoder at aviationWeather.gov seems to ignore the question mark & decodes it as if it were just "SHRA" rather than "?SHRA". I'm hoping to see if any jurisdiction besides FAA-land uses that punctuation to coney information -- I'm pretty certain that in the US, it'd just be a typo if it shows up.  I realize that I may be asking for somebody to "prove a negative" here, which may be tough.  A lack of any "yes" may be all the answer I can hope for.

In METARs, a question mark indicates that the reading is not reliable.  Presumably the equipment is throwing error codes and needs maintenance.  Maybe this pertains to TAFs as well?

A TAF isn't a reading, but rather a forecast; the lack of a rain/visibility/whatever sensor removes that value from a METAR report, but a forecast should still be able to predict all those thing, I'd expect.

There are no question marks nor any reference to them in neither the ICAO Annex 3 nor the WMO 306 Manual on Codes. These documents are the standards used for meteorological reports and forecasts in aviation. There might be national exceptions to these though.

Where might one find national exceptions? Specifically, for the Dominican Republic & the Bahamas -- those seem to be where the question marks (the D.R.) and other nonstandard punctuation (slashes in Bahamian METAR reports) often show up.

I don't know, but my bests guess is the (national) Aeronautical information publication (AIP). Maybe you could ask the local weather briefing if such is available


text:
How does a typical passenger jet come to a stop when it lands
Do the pilots of the plane simply reverse thrust of the engines after touchdown or are there brakes on the landing wheels that slow the plane just like a car? Or a combination of both?
What about prop-planes?

I think what you're really asking is how an aircraft is brought to a slow enough speed to safely exit the runway onto a taxiway. That's generally accomplished by both brakes and reverse thrust. Stops on the runway are to be avoided as it ties up the runway. Stopping at a parking gate/place is done by brakes. There are brakes on the main landing gear. Some aircraft have nose wheel brakes as well.
Turboprops typically have reverse thrust capability. Piston engine prop planes typically do not.

@Terry or the tug breaks for them while it's attached.

@ratchetfreak True, however I was thinking of the initial stop that would have been necessary to attach the tug, for which I should have noted.

The main components that stops the aircraft are the brakes and spoilers and secondary would be the reverse thrust and flaps.
When a airplane lands it still has some velocity and that velocity still creates lift.
When the spoiler goes up it stops the wing from create lift and sits the plane on the ground, so the brakes have more efficiency.
Some aircrafts would need twice or three times longer runways to stop with the spoiler inop.
As a secondary resource there are the reverse thrust and the flaps, witch when is full down creates more drag than lift and helps the aircraft to stop.


text:
Is it possible to isolate COM1 and COM2 on a Garmin G1000?
Is it possible to isolate COM1 to one pilot and COM2 to the other pilot?
When I'm getting the ATIS it's hard to listen to both COM channels sometimes depending on the amount of traffic.
I used to be able to do this on an older aircraft I flew, and loved the feature in a crew environment.

(wikimedia.org)
On the audio panel installed between the two G1000s, there should be a COM 1/2 key. That will enable the split COM operation with COM1 going to the pilot and COM2 going to the copilot.  What avionics are in the aircraft that you have?

Split COM allows the pilot to use COM1 while the copilot uses COM2. This proves very helpful for talking to an FSS en route without leaving the ARTCC frequency. Pressing the COM 1/2 key on the audio panel turns on Split COM mode (Garmin).

I've tried that button, it doesn't seem to work, I'll try it again tomorrow.  My company probably didn't pay for that feature to work.. :P

Interestingly enough, the G1000 Cessna NAV III manual (page 98-99 at http://static.garmincdn.com/pumac/190-00498-07_0A_Web.pdf mentions that the COM1/2 button is not used in the NAV III aircraft.  Which is weird because I thought I had used it... maybe I'm misremembering.  What A/C are you using the G1000 in?

I'm using it in the Cessna Grand Caravan

Different Aircraft manufacturers actually integrate the modular G1000 hardware and software into their aircraft. In doing so, each manufacturer has a large amount of control as to what features are actually enabled on their avionics in any particular type or airframe. An example of this is the Cirrus Perspective package which is basically a customized G1000 or the Cessna Nav III package used in Cessna 172S’s.
A good example of an aircraft manufacturer  customization related to what you are mentioning is Cessna’s disabling of the split com (COM 1/2) function, COM 3/COM 3 MIC, PA, TEL, and several other buttons in the Cessna 172S Nav III. You can find an online POH to review this info - the POH describes which functions are disabled.
Bottom line: each aircraft manufacturer gets to pick what works in both hardware and software to a certain degree even though the G1000 hardware and base software is the same.

@Brad I thought my answer was pretty complete for your question!

Cessna seems to have disabled it on the Grand Caravan...


text:
What is the cost of the engine Boeing 747 Model 400?
What is the cost of the engine Boeing 747 Model 400?
Including what component of the cost of the aircraft engine Gies

I do not really understand

cost of aircraft: 747-400/-400ER: USD234–266.5 million
747-400F/-400ERF: USD238–268 million

What does "Including what component of the cost of the aircraft engine Gies" mean?

200 million dollars is the cost of a 747 engine?
How much does the whole plane?
I read somewhere Arbus 380 exceeds $ 400 million
Including engine and chassis .....

The engines are the cheap part, with the engine manufacturers making their money on the spares and support during the life of the aircraft. As I understand it there have been cases of airlines receiving the engines for free when a manufacturer wants to get a foot hold in that airlines engine requirements (and depending on the actual fuel consumption of the engine and other costs over its life, the airline could find taking a free engine deal is a really bad idea).

The actual prices paid for an engine are likely to not be released publicly. However, list prices are advertised, and other sources may help give an idea of the price range for such engines. The 747-400 model has three engine options available: PW 4056, GE CF6, and RR RB211. These engines are also used on other aircraft, which will help in finding the prices.
The CF6 engine has a list price of about $11 million (from an A330 order in 2009, higher thrust version; \$12.2 million in 2015 USD1).
The PW4056 engine has a price of $5.8 million (from a 1994 report; \$9.3 million in 2015 USD).
I haven't found good pricing for the RB211. An older, lower thrust version was priced at £340,000 in 1971 (\$4.8 million in 2015 USD2), or you could buy one right now for $35,000 (the seller hopes it can be put on display, mentioning "very high end art displays" but also "top dollar in scrap").
The list price for a 747-400 was about \$240 million, which means that 4 engines at a list price of \$10 million each would be about %17 of the cost of the plane.
1Inflation calculator
2exchange rate

Do they get a discount, like buy one engine, get one free?

Just to point out the obvious, $ 5.8 million in 1994 dollars is quite different from $ 5.8 million in 2009 or 2015 dollars.

Also, this is probably obvious, too, but the RB211 on eBay is presumably not in working order (it's being sold as a display exhibit, not as a functioning engine.) Still, nice find. :)


text:
Who decides the regular procedure followed by the pilots before takeoff?
Pilots need to go through a checklist before they take off. Are these procedures decided by the airlines and (or) the manufacturer, or by the Civil Aviation Regulatory Authority of the respective country?

This begins with the aircraft manufacturer. Note that checklists are not the full story. Checklists are only a small recap of what should have been done. See Flight Crew Training Manual for the A320 (e.g. page 79) for an idea of how this works.

Similar: Regular procedure followed by the pilots before takeoff?

The manufacturer will publish a checklist.  Some airlines will choose to use the manufacturer's checklist verbatim, while others will adapt it to their specific operation based on things like safety reporting data from their fleet.  The end result will need to be approved by the regulating authority (in the US, the FAA -- specifically the Certificate Management Office or CMO for that airline) before it's used by crews.
An example of how an airline might modify the checklist would be to adapt it in light of new Human Factors research.  Telling crews to "run this checklist" during some large interval of time (say, between leaving the gate and reaching the runway, or between leaving cruise altitude and starting the approach) can lead to a missed checklist, and research recommends "anchoring" the checklist to some cue that's unlikely to be missed.  So, "run THIS checklist before you release brakes and start to taxi, and THIS checklist when you have about 2000' left to taxi before reaching the end of the runway, and THESE 3 items as you take the runway for departure" gives crews anchor points that they'll observe anyway and leave them less likely to look back and wonder "did we read the Before Takeoff checklist?"
The manufacturer might have made it all one long 15-item checklist that they have crews read "whenever," but the airline could separate out the items that are best accomplished before starting to taxi (knowing that the more items you put here, the longer the delay before the aircraft starts moving), the items that can be accomplished while taxiing (probably not stuff that requires a lot of 'heads down' time like reviewing the FMC routing), and the items that should be delayed until immediately before departure (strobes lights, landing lights, radar etc).

Obviously the manufacturer knows the human factor research too and can prepare the checklists/procedures so that it takes them into account. So why would the airlines want to tweak them differently?

The manufacturer's checklist that I've seen tends to be pretty general. It covers what you must do to operate the airplane, but it's not necessarily the most efficient way to do it. Say you always start on a hardstand, & when you leave the hardstand you're at the runway within a minute. That case drives a different solution than if you typically push back from a gate, sometimes very close to a runway and sometimes very far. Say 1 operator always flies in the US where transition level is always 180 - anchor "descent checklist" there. Another has trans lvl between 190 and 020: different needs!

Another reason, in some cases: airline A has Airbus + Boeing + McDonnell Douglas aircraft, with pilots regularly transitioning between them. The FAA would require a level of standardization across fleet types, so if that standard is "Before Descent Checklist" before top of descent & "Approach Checklist" at 10,000', then that's what they'll all have. Airline B with all Boeings, doesn't have that constraint.

The comments may be worth editing into the answer.

For commercial flights run by carriers or charter companies, the company makes the checklists. These will be based on the manufacturer-recommended checklists.
Pilots working for small companies or flying individually make their own standard operation checklists. Usually when a pilot starts flying a type they will use either a manufacturer checklist or a commercially published checklist. Then, at some point the pilot may make minor changes for various reasons.
For non-normal operations (emergencies), the manufacturer checklists are used verbatim.


text:
Is it possible for a Citation Jet not to have an APU or AIR COND?
In reviewing a number of CESCOM10 reports it has become apparent that some of the aircraft don't report APU hours (instead they report AIR COND).
Is it possible that a Citation Jet doesn't have an APU?
For those reports that do report APU hours, no AIR COND hours are reported ... is it possible that there are Citation Jets that have APUs and no AIR CONDs?

Are you asking for a particular Citation airframe, I Imagine the answer may vary across the model line as "Citation" encompasses a variety of airframes.

If it has pressurization, it has air conditioning.

@RalphJ But not necessarily a freon AC system that might require reporting.

I think that systems with APU typically don't have independent AC systems that need to be tracked for maintenance purposes which is why you never see any CESCOM10 reports that have both APU and AIRCOND hours.  Conversely, without an APU, there is typically some kind of AC system that is independent and therefore tracked.

It is possible for a Citation jet to not have an APU, two of them that come to mind are the CJ2 and CJ3 aircraft. An aircraft with an APU can have an independent air conditioning system or not, it just depends on the installation and manufacturer. Some airframe manufacturers use engine (or APU) bleed air to condition the cabin air temperature. Something like an APU would have overhaul limits similar to an engine, propeller, or a combustion heater like in smaller aircraft. Anything with a life limit would have to be tracked, so that could be individual components of a larger system, such as the starter/generator of an APU, or a compressor motor of an air conditioning system. I think what you're seeing is a coincidence.

A very large number of Cessna Citations do not APUs including (but not limited to):
CJ (Although actually a CitationJet)
CJ1
CJ1+
CJ2
CJ2+
CJ3
CJ3+
CJ4
CE500 Citation
CE501
CE550
CE551
CE560  (not including the CE-560XL)


text:
What is the equivalent of Hobbs and Tach in a Jet or Turbine Aircraft?
As a piston pilot I am only familiar with tracking hours for my pilot log book and maintenance log book using the Hobbs and Tach times.  Can someone tell me what the equivalent is for a Turbine and for a Jet?

We used clock time to track Metroliners and hobbs to track a Turbo Commander.  I think hobbs is acceptable if installed.

Related

Any installed time tracking system will be acceptable for logging maintenance times. Under FAA regulations, mechanical or electrical time tracking systems in aircraft generally do not keep track of "flight time" which is what is to be logged or kept track of. See 14 CFR 1.1 In the turbine I fly we log time based on block to block time, which is the same as FAA defined flight time in our case.

In all of our jets, we have two hobbs meters. One is active from left engine start and the other goes active when the weight of the aircraft leaves the wheels. Neither of these are used for logging our flight time. We do that "chock-to-chock", ie as soon as the chocks are pulled and we start moving to when the chocks are put back in the wheels.
The regs say you can log flight time from when "the aircraft moves under it's own power for the purpose of flight":

Flight time means:
  (1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; or
  (2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.

Which of those measures are used to track total time for maintenance purposes (e.g. phase inspections etc.)?

We use WOW for all maintenance.

I'm sorry for my ignorance, what does WOW stand for?

Sorry about that - it stands for Weight on Wheels.


text:
What software generated this VFR flight plan?
I recently came across this screenshot of a VFR flight plan.  Does anyone know what software was used to generate it?

this must be skyverctor.com

Out of curiosity, why the Off Topic votes? Questions to recommend a software package to accomplish some task would be off-topic, but this one is just asking what piece of software generated this particular image, which is objectively answerable and related to aviation.

This flight plan was generated with Skyvector
Click here for the specific flight plan from your example
Then click "Nav Log" for the log itself.


text:
How low was the Hong Kong Kai Tak landing approach over the city?
Hong Kong's Kai Tak approach was famous for its unique approach, including the "checkerboard" and its low altitude when passing over Kownloon.  The latter has been memorialized in innumerable photos and film clips.
At what altitude did landing aircraft typically pass over the city on this approach?

This looks like a question for @Terry

As the wikipedia article for Kai Tak, Runway 13 approach states:

Typically the plane would enter the final right turn at a height of about 650 feet (200 m) and exit it at a height of 140 feet (43 m) to line up with the runway.

Given that some of those buildings underneath the flightpath were 6-storey and therefore ~60-70ft tall, the aircraft were less than 100ft above the highest rooftops. (This I can personally vouch for, since my sister did for a while live in one of those 6-storey apartment buildings and I have stood on the rooftop watching the planes pass over!)


text:
Does the FAA have risk targets for specific activities?
Does the FAA have or publish goal values for various risks?
I'm looking for something that says (e. g.) "We rate passenger airline flights as 'safe' if there are fewer than X casualties per million flying hours" or the like.  Even better would be some kind of matrix reflecting "safe", "of concern", "hazardous", "dangerous", etc.

Possibly related: https://aviation.stackexchange.com/questions/46677/what-are-the-design-parameters-for-airliner-safety

@Erik that's more of a system level risk and failure analysis that drives system design.  Mark is after more generic "public" risk factors I think.

I believe that what you are looking for relies on aviation's systems probability of failure occurrence. For instance, catastrophic failures that can lead to fatalities cannot occur more than 10e-9 per flight hour for commercial aviation. Does this answer your question?

@ppinto, I think that's what I'm looking for.  Are these specifications published somewhere?

@MarkHarrison It can be found in standard ARP4761, page 14. I can prepare an answer to this question showing it.

I know I've seen a specific statistic cited when the FAA decided not to require transponders on sailplanes and other aircraft without engine-driven electrical system-- they said the risk of a castrophe was less than X and therefore we won't require them-- can't provide an  exact source right now.

"We rate passenger airline flights as 'safe' if there are fewer than X casualties per million flying hours"
I am not aware of any official FAA document that states such sentence. However, something similar can be deduced from safety requirements related to the development of aviation systems.
ARP4761 is a well-known standard for conducting safety assessments on civil airborne systems and equipment. A probability of failure occurrence associated with the severity classification can be found on page 14, which shows the following table:

As it can be seen, the maximum allowed occurrence of a catastrophic failure is 1.0E-9. Playing a bit with the numbers, this could be translated in:

Commercial aviation flights are considered as 'safe' if there are fewer than 1 catastrophic condition per billion flight hours

One could assume that a catastrophic condition can lead to fatalities, and this seems reasonable. But I'm afraid that this presumption is not written in official FAA publications (I might be wrong).

P.D.: Now, where these probabilities of occurrence come from is another interesting (and un-official) story, but I think is out of the scope of this question for the moment.


text:
What aircraft was used as Air Force One for the flight between Southampton and Shannon?
On Wednesday 5th June 2019, The US President flew from Southampton Airport, UK to Shannon Airport, Ireland on Air Force One.
However, since SOU is more of a small regional airport, more used to seeing Dash-8s, the runway isn't very long so the aircraft used wasn't the usual B747-200, it was this much smaller aircraft.

Can anyone identify the type? My guess would be a B737-600?

The "drooped" appearance of the nosecone is one quick clue that it is not a 737--

Boeing windscreen (and it'd be funny if the POTUS used an Airbus), four-wheeled main undercarriage and four grown-up doors => 757 or 767, nosewheel underneath front door => clearly a 757

The sheer amount of "stuff" has travels around the world with the POTUS is frankly shocking. How many planes does one person need!?

:-O I didn't realise that Air Force One was more than one plane! Is AF1 basically whatever plane the president happens to be using?

@AaronF Air Force One is any Air Force plane on which the President happens to be at the time. If the President is not on board, it is not Air Force One, but rather goes by something like "SAM " (SAM stands for "Special Air Mission.") The primary planes used as Air Force One are the VC-25s (the modified Air Force Boeing 747s,) of which there are two. But the C-32As get used as Air Force One somewhat frequently as well, particularly when the President needs to fly somewhere without a runway long enough for the VC-25s.

@AaronF If the President is on an aircraft that isn't owned by the Air Force, then it's called " One" if it's a different military branch (e.g. "Marine One," "Navy One," etc.) or "Executive One" if it's a civilian aircraft. This is why the Presidential transport helicopter (which is owned by the U.S. Marine Corps) is called Marine One when the President is on board.

As Bianfable mentioned, this is the C-32A, which is the U.S. Air Force's transport variant of the Boeing 757-200.
In this case, due to the shorter runway, they used the C-32A instead of the iconic VC-25, which is the Air Force's VIP transport variant of the Boeing 747-200 that is typically used for transporting the President of the United States.

U.S. Air Force C-32A. Image Source: Wikipedia
The C-32As are mostly used for transporting the Vice President of the United States as "Air Force Two" as well as members of the President's family and other high-level government officials.
However, the President may use the C-32As when flying to airfields that are too small to adequately support the monstrous VC-25s. The short-field performance of a 757 — especially a VIP-configured one — is quite good, so it can use runways that are relatively short for a plane of its size. It is also capable of making trans-Atlantic hops non-stop from the U.S. East Coast (indeed several airlines use the 757-200 to do that with much more dense passenger loads.)

@ymb1 Hmm... I can't seem to find an exact squadron for the VC-25s from a quick search, but it looks like they're part of the 89th Airlift Wing, of which the 1st Squadron is also a part. The 1st Squadron's wiki does say that they are assigned to the Special Air Mission, including transporting the President, but you're right that it makes no mention of the VC-25s, which would be a very odd thing to leave out if they operated them.

@ymb1 Ah, the wiki for the SAM lists a separate "Presidential Airlift Squadron," so I'd guess that probably operates the VC-25s.

It is a Boeing C-32, which is the military variant of the Boeing 757-200.


text:
Does the FAA Publish the Latitude/Longitude of Parking Locations?
In Jeppesen charts, it's known that they provide the latitude/longitude of gate locations at airports. I was wondering if the FAA had a source for the same information, like their international counterparties.
Would anyone know if the FAA keeps that data somewhere? Is Jeppesen extracting the parking locations themselves and putting those in their Navdata and Charts products?

Stand location is collected as AircraftGateStand for airport certification, see AC 150/5300. It should be possible to get this information, after discussing with FAA.


text:
How do modern helicopters tackle Vortex Ring State?
According to the wikipedia page :

Air vortices can form around the main rotor of a helicopter, causing a dangerous condition known as vortex ring state (VRS) or "settling with power". In this condition, air that moves down through the rotor turns outward, then up, inward, and then down through the rotor again. This re-circulation of flow can negate much of the lifting force and cause a catastrophic loss of altitude. Applying more power (increasing collective pitch) serves to further accelerate the down wash through which the main-rotor is descending, exacerbating the condition.

The vortex ring state has also been listed as a potential hazard in the Wikipedia page for helicopters. What are the various preventive measures used to prevent such a condition?

Vortex ring state and settling with power are two different things. For example,  one can also settle with power in high density altitudes or in OGE hovering

VRS from the high compound walls is attributed as the cause of the helicopter crash in the Bin Laden operation (https://en.wikipedia.org/wiki/Death_of_Osama_bin_Laden).  Since that was a state of the art U.S. military stealth helicopter, it seems likely that it would've had VRS countermeasures, if any existed.

There's an interesting article on the hazards at wikipedia.
The avoidance tactic mentioned in that article is to avoid rapid descents at low forward airspeed - this would seem sensible as that's where the rotors will be exposed to their own downwash.
And the preferred reaction also described there is to use the cyclic to fly forwards, to move into less disturbed air.
(I have heard that another cause of the condition is flying into narrow spaces among tall buildings, but unfortunately I haven't been able to find a reference.)

Flying forward is sometimes correct but there are other recoveries which would be more appropriate in certain circumstances.  In essence, either stop the recirculation, e.g. enter auto-rotation, or fly out of the descending air in any direction.

Narrow/Tall buildings causing VRS: The high compound walls were what caused VRS and the helicopter crash in the U.S.'s Bin Laden operation: https://en.wikipedia.org/wiki/Death_of_Osama_bin_Laden

this is definitely the wrong answer

Helicopter driver here.
I am not aware of any technical features which can prevent it.  Quite simply, the disc must accelerate air downwards to generate lift.  If the helicopter descends into that downward accelerating air, it is recycled through the disc resulting in a catastrophic loss of lift.
The preventative measures are:

Be aware of the flight conditions under which vortex ring state may occur.
Do not fly into these conditions.
Be able to recongise the symptoms of vortex ring state.
Understand, and be practised in, the correct recovery technique, which is most often fly in any direction away from the vortex.

I am not an aerodynamics engineer but I doubt that there is a physical solution to this - and if there was, it would likely have been implemented by now.

I would recommend to land with some forward speed, either provided by wind or by motion of the craft. This might not work in tight conditions, but then the vortex ring will also be weaker.

@PeterKämpf I'm not sure I understand your comment.  If you have flown out of vortex ring, then you just land normally.  If you haven't, then you don't get to choose how to land :)

I meant to make sure there is a horizontal flow component when landing, as a precaution. Once you are in a mouse trap, it is hard to get out again.

@PeterKämpf ah, I see, you mean avoid it?  Yep, on my most common types, avoid <30 kts when >300 fpm.

And avoid downwind landings.

@rbp The helicopter doesn't know it's downwind, only the relative airflow matters, Avoid low air speed and high ROD with power on and you won't get into VRS.  Of course, the downwind component means a higher ground speed but your airspeed will be the same.

No Simon. The issue with a downwind landing is that you lose transnational lift on short final.

@rbp Yep, but that as long as you have HOGE power and your ROD is minimised, you still won't get into VRS.  If I fly with > 30 kts airspeed, with a tailwind (and ignoring the problems with aft cyclic authority and weathercocking) then I can land with no risk of VRS.  I've got lots of other things to worry about and I need a lot of room to skid to a stop but being downwind does not change the incipient entry conditions for VRS.  The problem arises because inexperienced pilots keep the same sight picture and apparent ground speed which leads to higher ROD and lower airspeed.

BTW, I'm not saying downwinds are OK, they aren't, they are truly dangerous for all but the pros and highly experienced, just saying that no matter where the wind is, keep airspeed up and ROD under control and you won't get into VRS.

from https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/helicopter_flying_handbook/media/hfh_ch11.pdf page 11-10:
The following combination of conditions is likely to cause
settling in a vortex ring state in any helicopter:

A vertical or nearly vertical descent of at least 300
fpm. (Actual critical rate depends on the gross weight,
rpm, density altitude, and other pertinent factors.)
The rotor system must be using some of the available
engine power (20–100 percent).
The horizontal velocity must be slower than effective
translational lift.

The left picture above from J. Gordon Leishman, Principles of Helicopter Aerodynamics, depicts the Vortex Ring State where the wake below the rotor is re-ingested on top of it. A dangerous situation indeed, since adding power may result in higher vortex velocities only.

In section 5.3 of the Leishman book a further detailed discussion of the VRS can be found. A quantification is given as induced power loss in VRS: measured data shows a power loss factor of almost 2 in some circumstances, and here lies one of the issues in trying to recover with adding power. The engine is simply not dimensioned to deal with such effective power loss.
Another problem is flow fluctuation, leading to fluctuations in thrust of up to 40% depending on disk loading:

The VRS is accompanied by an extremely unsteady (aperiodic) flow field surrounding the rotor.

All in all a dangerous situation to be in, since the flow fluctuations associate with a loss of predictability. Best avoided, although one of the methods to recover is to reduce rotor Angle of Attack:

Notice that the fluctuations drop off quickly as the disk AoA decreases below 50° and is consistent with piloting experience on helicopters, which shows that a forward speed component causes the rotor to quickly exit the VRS.

After tuning the flight controls of a CH-53 helicopter simulator and going for a test ride, I inadvertently got the sim in a VRS in the thin mountain air surrounding the modelled airbase. The instructor told me to give full left lateral, wait for the helicopter to reach a considerable roll angle, then full right lateral, then mid again; then regain horizontal attitude while pressing cyclic forward. The initial lateral movement indeed changed the disk AoA enough to exit the VRS quite rapidly.
I don't know if this is taught as a recovery practice in the real helicopter though, or if it only works in the (high fidelity military) simulator.

Late reply, but I wanted to bring attention to this very excellent video that shows vortex ring state, using a helicopter with a sprayer, spraying a mist of water to visualize the airflow around the rotors. At about 2:28 into the video, that helicopter enters vortex ring state, and you can see exactly what happens to the airflow over the rotors.
When the helicopter descends too quickly with little or no forward airspeed, the downwash curls around and breaks up the airflow on the top of the rotors. The end result is much the same as breaking up the airflow over an aircraft wing, like an aircraft with insufficient forward speed and a high angle of attack... it kills most of the lift. Essentially, the blades stall, and the helicopter drops even faster.
Pulling up on the collective would do the same as pulling back on the stick a stalled aircraft... it would just make a bad situation worse.
The solution is to get out of the turbulent airflow, by either tilting the helicopter forward, or in the video that demonstrates the Vulchard technique, tilting to one side. As you can see in the video, the helicopter recovers fairly quickly, and the mist illustrates how tilting to one side restores smooth airflow on the tops of the rotors, enough to arrest the too fast descent.
Or, as Simon notes... the better solution is to know your aircraft and not allow it to get into VRS in the first place... just as with fixed wing aircraft, you're well advised not to let it get into a stalled condition.

There are four factors:  low airspeed less than 20 knots, partial power, high rate of descent greater than 300-500 feet/minute, and steep angle of descent greater than 30 degrees.  Somehow, the aircraft has to descend, either by settling or other means at great than 30 degrees.  Remove any of these four items and VRS is not possible.

The last "factor" is no factor at all. If you are at <20kias and >300fpm descent, you are by definition making a steep approach.

For which model of aircraft are you making this assertion?  The disc loading will change the RoD value for incipient VRS depending on a number of factors.


text:
Why do jets with 3-D thrust vectoring never hover nose up, but instead move slowly forward?
I've seen several impressive videos of fighter aircraft moving incredibly slowly by essentially hovering on the engines, balancing using thrust vectoring. For example:
This Su-10
This Su-37
Large RC jet aircraft often take this maneuver one step further, by coming to a complete stop in the air before accelerating away. Do airshow pilots choose not to attempt to come to a stop because it's too dangerous, or is there some hardware difference between RC jets and military jets that limits their ability to hover in place?

There are limitations in the ability to articulate the thrust vectoring that would limit the ability to hover in space and requires some small amount of forward speed to keep the Sukhoi in a controllable state.  It looks like the RC jet has a vector nozzle that can operate in all directions so that it can be hovered in place like a helicopter, although I imagine the skill level on the part of the operator is pretty high.
My favourite airshow performance of all time was a guy, Wayne Handley, with a monoplane aerobatic machine, the Turbo Raven, with a PT-6 engine, which had a thrust to weight ratio of well over 1:1.  The elevator and rudder surfaces allowed him to control attitude while hanging on the prop, and the ailerons provided anti-torque control.  At Osh in 1998 or 99 I remember him hovering in front of the crowd, moving around in a square box pattern, like outlining a picture frame in the sky, then accelerating straight up until he was a speck.  He stopped doing the act after a crash, from the prop not wanting to come out of ground beta during a descent maneuver, about a year later.  Never seen anything like it since.


text:
How does ATC control traffic without radar?
Clearly, it is necessary and possible for ATC to control air traffic without radar:

not every control tower has a radar feed from a TRACON or their own radar site
over the ocean, aircraft are beyond the range of radar for long periods of time
Going back several decades, large stretches of domestic airspace in the US didn't have radar coverage

What are the methods by which air traffic is controlled and managed without radar?

Without radar or other surveillance technology (such as Wide Area Multilateration, ADS-B), ATC uses procedural control.
In procedural control, air traffic controllers build up situational awareness by using pilot reports, estimates and visual observations, combined with knowledge of routes, navigation beacons, fixes and other reporting points, plus support tools such as flight strips.
ICAO Doc 4444 (PANS ATM), Chapter 5 contains the procedures and procedural separation minima to be applied by ATC.
The separation minima for procedural control are much larger than for radar control (typically 5 NM or 3 NM), and are often expressed in minutes (e.g. 15 minutes).

Example of procedural separation minima from Doc 4444, showing 15 minutes or 10 minutes separation minima, depending on the presence of navaids. Source: ICAO Doc 4444


text:
Why are turbofan inlets leaned/angled forward?
(Image Source: Wikipedia)
Seeing that everything is radially symmetric (apart from the nacelle mount, naturally), I wonder why the inlet (the front part of the nacelle) is usually skewed?

I'll let the tech guys like Peter Kämpf answer that, but from the hip, I would say this is because during cruise flight, you will maintain a positive angle of attack / pitch that will make the inlet vertical again. But that is a mere assumption...

@mins: It's a Rolls Royce Trent 1000 engine on a Boeing 787 Dreamliner plane.

@mins: RR currently have 50% market share of the widebody airliner engine market.

ahh okay. I was wondering if there was the Spirit of Ecstasy on the plane nose :-)

I'd appreciate if the downvoter left a comment as to what is wrong with this question.

The inlet angle is a compromise between cruise, when the aircraft has a low angle of attack, and the take-off and climb phase, when the engine runs at maximum thrust, and the angle of attack is several degrees higher than during cruise. Especially right after rotation, when the aircraft is heavy and slow, the angle of attack might reach into the lower two-digit territory, and flow disturbances must be avoided especially in this phase.
Note that the fuselage should be horizontal during cruise to avoid making the work of the cabin personnel harder than it already is. A few degrees of intake misalignment can be tolerated, and the misalignment is usually split between cruise and post-rotation climb.
With supersonic intakes, things are different: They are much more sensitive to misalignments, and the intakes of planes like the SR-71 have been carefully optimized for their cruise condition.

Thank you for your very fine ansver! Coming to think of it, almost every shape on an airplane is a compromise, isn't it? But the tradeoff between climb and cruise really didn't cross my mind.

What about the upwash of the wing? See the answer that I just posted.

@Daniel: Yes, there is upwash, but not as far forward as the engine inlets. In cruise the typical upwash angle is just 1.5° (but far more during take-off and landing).

I'm quite suprised that this wasn't mentioned in any of the previous comments or answers, but since the inlet is quite far in front of the wing, it sees some significant upwash from the wing. To align the inlet with this local flow direction, it is slightly angled down. For the same reason the engines on Bombardier CRJ series aircraft are slightly angled upwards! The other answers are correct as well though, this is just an additional element.

It makes a lot of sense!